Time for some new Kamen Rider Build rumors as the bringer of tokusatsu rumors, Dukemon, gives us the latest take-a-grain-of-salt news involving the additional riders, gears and weapons.
According to this post from Ranger Board, an alleged Kamen Rider Build toy listing has surfaced and gives us the following infos:

Transformation belt will be called "World Driver", additional riders will be called Kamen Rider Pain (painter?) and Kamen Rider Roots (gardener?) and Build will be armed with SaibattoBlade. The new gimmick for the series will be called "Material Bottles".

Again, these are rumors and you should take this with a grain of salt.